(A) Field of the Invention
This invention relates to the preparation of metahydroxybenzoic acid (m-hydroxybenzoic acid) by fusion of metasulfobenzoic acid with an alkali metal hydroxide and more particularly relates to a method for recovering m-hydroxybenzoic acid from the fusion reaction mass.
(B) History of the Prior Art
In the prior art, it was known to dilute a reaction fusion mass used to prepare m-hydroxybenzoic acid alkali metal salt followed by acidifying the resulting solution to crystallize m-hydroxybenzoic acid (see e.g., U.S. Pat. No. 3,468,942; U.S. Pat. No. 3,094,558; Kirk-Othmer Volume 17, 2nd Edition, page 736; American Chemical Journal, 1912, page 432 and Justus Liebig's Annalen Der Chemie, Volume 280, 1894, Kekule et al.)
The products resulting from isolation by dissolving the fusion mass for preparation of m-hydroxybenzoic alkali metal salt followed by crystallization of m-hydroxybenzoic acid from the resulting solution by acidification frequently contains substantial quantities of isomers of hydroxybenzoic acid other than the meta isomer. In particular, an undesirably large quantity of parahydroxybenzoic acid is often present. It was therefore frequently necessary to recrystallize the m-hydroxybenzoic acid initially obtained from the dissolved fusion mass in order to obtain a m-hydroxybenzoic acid product of the desired purity. Such recrystallizations frequently result in loss of yield due to the solubility of the m-hydroxybenzoic acid in the crystallization medium.